Patent GB-1376417-A (GB)
Title: Hydro-pneumatic brake control system
IPC: B60T13/44
Filed: 1973-04-06
Abstract: 1376417 Spring applied fluid pressure released brake systems BENDIX CORP 6 April 1973 16718/73 Heading F2F A brake control system has a spring-applied hydraulically released vehicle parking brake mechanism housed within a disc brake caliper 98, hydraulic fluid to release the brake being supplied via a control valve 88 from a pressure intensifier 10 and both the intensifier 10 and the control valve 88 being connectible to an air pressure reservoir 16 by operation of a driver's control valve 120 so that air pressure controls the hydraulic release of the mechanism. The intensifier 10 includes a recycling valve 12 having an inlet port 14 connectible to reservoir 16 and an outlet port 17 connected to an inlet port 18 communicated with a compartment 20 within the intensifier 10. The compartment 20 is divided into two sections 40, 42 by a movable wall 36 and a rolling diaphragm 38, the movable wall 36 being carried by a piston 24 which defines a pressure chamber 22, the pressure chamber 22 communicates with an hydraulic reservoir 30 via a valve 32 and a port 28 and with the control valve 88 via an outlet port 26. The control valve 88 has an inlet port 114 connectible to air reservoir 16 to communicate air pressure to a pressure chamber 112 below a piston 100. A rod 108 projects from the piston 100 through a closure 110 and abuts a sphere 118 of a valve 116, 118 interposed between ports 94, 96 of the control valve; the port 94 connects with outlet port 26 of intensifier 10 and the port 96 with the parking brake mechanism. With the mechanism applied the components take up their positions illustrated in Figs. 1, 2. To release the parking brake, the driver operates valve 120 and air pressure communicated to chamber 112 acts to move piston 100 upwardly to close valve 116, 118. Thereafter fluid communication from port 96 to port 94 is prevented but communication from port 94 to port 96 is permitted. Air pressure is also communicated to port 14 of recycling valve 12 and through openings in a valve element 50 to port 17 and thence to port 18. The fluid pressure thereafter acts to move wall 36 and piston 24 rightwardly; as the piston 24 moves it first closes valve 32 and thereafter pressurizes the hydraulic fluid in chamber 22 which is communicated to the brake mechanism via ports 26, 94, 96 to cause release of the brake. As the wall 36 moves rightwardly the diaphragm 38 unrolls-it first of all covers a passage 84 to cut off communication between an annular control chamber 58 and the exterior of the recycling valve housing 44, and thereafter opens a valve 74, 76 to communicate control chamber 58 with inlet port 14. Air pressure acting in chamber 58 will then move a piston 48 leftwards, the valve element 50 follows it to close a valve 64, 122 and cut off ports 14, 17, and as piston 48 moves away from valve element 50 port 17 is connected to an exhaust port 60 via a passage 124 extending through piston 48. Thereby fluid in section 40 of intensifier 10 is exhausted and the wall 36 and piston 24 move leftwards again. However, as the movable wall 36 moves leftwardly air pressure is again communicated to section 40 and the intensifier cycles again and this is continued until the pressure in the brake mechanism equals the air pressure in section 40. To operate the mechanism when the vehicle is parked the valve 120 is operated to vent ports 14, 114 to atmosphere whereupon section 40 and chamber 112 are vented and the pressure in the mechanism is reduced to allow of spring application.